Youth with autism spectrum disorders (ASD) are at high risk for anxiety and sensory over-responsivity (SOR), which cause significant impairments in adaptive behavior and social functioning independent of ASD severity. While emerging research shows an association between these two syndromes in children with ASD, little is known about (1) the mechanism that links them, such as a common neurological basis, and (2) implications of this association for the treatment of children with ASD. It is possible that anxiety and SOR have a similar neural basis, such as amygdala and hippocampus abnormalities, but the brain structure and function of children with ASD and SOR has not been examined. Findings of a similar neural basis might support a coordinated diagnosis and treatment approach for anxiety and SOR in youth with autism. The proposed study takes a two- pronged approach to improve the understanding and treatment of these two syndromes: the first is a basic science approach to identifying putative common neural abnormalities underlying anxiety and SOR, and the second is a treatment design to examine whether the connection between anxiety and SOR has real-world implications for intervention. Participants will be 68 children with ASD, aged 10-14 years, recruited from the UCLA Center for Autism Research and Treatment (CART) into ongoing imaging studies at the UCLA Brain Mapping Center. Children who are above the cutoff for significant anxiety on a standardized anxiety interview (approximately 38) will be enrolled in an ongoing cognitive-behavioral treatment (CBT) intervention for youth with ASD and comorbid anxiety disorders. The proposed study will examine amygdala and hippocampus volume as well as brain response to mildly unpleasant sensory stimuli in relation to symptoms of SOR and anxiety. Additionally, this study will test whether symptoms of SOR improve over the course of CBT for children with ASD and anxiety, and whether improvements in SOR correspond with improvements in anxiety. This work will contribute to the field by facilitating understanding of the nature and impact of anxiety and SOR in autism, with possible implications for the development of a more effective and efficient treatment approach for these two related syndromes. These aims are consistent with the aspirational goals of the 2009 Interagency Autism Coordinating Committee Strategic Plan for Autism Spectrum Disorder Research, which stipulates the need for biobehavioral studies of ASD to identify and characterize co-occurring symptoms.